regex capture group names must use identifier syntax

Prior to this commit the non-first characters could be any \w character.
But an identifier excludes a few \w characters from appearing in them.
This commit tightens what is allowed.

Commit xd1e2a852fbc901b45fba20906a8f42ca227ae462 gave a list of them,
but I forgot a couple details in generating that list, so it wasn't
quite right.

The complete corrected list is:
GREEK YPOGEGRAMMENI
COMBINING CYRILLIC HUNDRED THOUSANDS SIGN
COMBINING CYRILLIC MILLIONS SIGN
COMBINING PARENTHESES OVERLAY
COMBINING ENCLOSING CIRCLE
COMBINING ENCLOSING SQUARE
COMBINING ENCLOSING DIAMOND
COMBINING ENCLOSING CIRCLE BACKSLASH
COMBINING ENCLOSING SCREEN
COMBINING ENCLOSING KEYCAP
COMBINING ENCLOSING UPWARD POINTING TRIANGLE
CIRCLED LATIN CAPITAL LETTER A - Z
CIRCLED LATIN SMALL LETTER A - Z
VERTICAL TILDE
COMBINING CYRILLIC TEN MILLIONS SIGN
COMBINING CYRILLIC HUNDRED MILLIONS SIGN
COMBINING CYRILLIC THOUSAND MILLIONS SIGN
ARABIC LIGATURE SHADDA WITH DAMMATAN ISOLATED FORM
ARABIC LIGATURE SHADDA WITH KASRATAN ISOLATED FORM
ARABIC LIGATURE SHADDA WITH FATHA ISOLATED FORM
ARABIC LIGATURE SHADDA WITH DAMMA ISOLATED FORM
ARABIC LIGATURE SHADDA WITH KASRA ISOLATED FORM
ARABIC LIGATURE SHADDA WITH SUPERSCRIPT ALEF ISOLATED FORM
ARABIC LIGATURE SALLALLAHOU ALAYHE WASALLAM
ARABIC LIGATURE JALLAJALALOUHOU
ARABIC FATHATAN ISOLATED FORM
ARABIC DAMMATAN ISOLATED FORM
ARABIC KASRATAN ISOLATED FORM
ARABIC FATHA ISOLATED FORM
ARABIC DAMMA ISOLATED FORM
ARABIC KASRA ISOLATED FORM
ARABIC SHADDA ISOLATED FORM
ARABIC SUKUN ISOLATED FORM
SQUARED LATIN CAPITAL LETTER A - Z
NEGATIVE CIRCLED LATIN CAPITAL LETTER A - Z
NEGATIVE SQUARED LATIN CAPITAL LETTER A - Z

Author: khwilliamson

regcomp.c

@@ -2532,7 +2532,7 @@ S_reg_scan_name(pTHX_ RExC_state_t *pRExC_state, U32 flags)
         do {
             RExC_parse_advance(advance);
         } while (   RExC_parse < RExC_end
-                 && (advance = isWORDCHAR_utf8_safe( (U8 *) RExC_parse,
+                 && (advance = isIDCONT_utf8_safe( (U8 *) RExC_parse,
                                                      (U8 *) RExC_end)));
     } else {
         RExC_parse_inc_by(1); /* so the <- from the vFAIL is after the offending

t/re/pat.t

@@ -28,7 +28,7 @@ skip_all_without_unicode_tables();
 my $has_locales = locales_enabled('LC_CTYPE');
 my $utf8_locale = find_utf8_ctype_locale();
 
-plan tests => 1296;  # Update this when adding/deleting tests.
+plan tests => 1298;  # Update this when adding/deleting tests.
 
 run_tests() unless caller;
 
@@ -1388,6 +1388,28 @@ EOP
             fresh_perl_like($prog, qr!Group name must start with a non-digit word character!, {},
                         sprintf("'U+%04X not legal IDFirst'", ord($char)));
         }
+
+        foreach my $char (chr(0x2115), chr(0x24B7)) {
+            my $prog = <<"EOP";
+use utf8;;
+no warnings 'utf8';
+print 0 + "abc" =~ qr/(?<a${char}b>abc)/;
+EOP
+            utf8::encode($prog);
+            if ($char =~ /\p{XID_Continue}/) {
+                fresh_perl_is($prog, 1,
+                                {},
+                                sprintf("U+%04X is legal IDCont",
+                                        ord($char)));
+            }
+            else {
+                fresh_perl_like($prog,
+                                qr/Sequence .* not terminated/,
+                                {},
+                                sprintf("U+%04X not legal IDCont",
+                                ord($char)));
+            }
+        }
     }
 
     { # [perl #101710]